1. Field of the Invention
The present invention pertains to the drilling and/or production of wells such as are used to recover petroleum and natural gas. During the course of such operations, various foreign bodies, such as tools or parts of tools, teeth which have become dislodged from drill bits, etc. may fall to the bottom of the well or may become lodged in the well some distance from the bottom. Such bodies, referred to as "junk", are frequently formed of hard metals or like material which can not readily be drilled through without damage to the drill bit. They must therefore be removed by other techniques before work on the well can continue. The tools used for removing such junk are commonly known as fishing tools or "junk baskets" and generally include means for engaging or collecting the junk so that, when the junk basket is withdrawn from the well, the junk is also removed.
2. Description of the Prior Art
There are three basic types of conventional junk baskets. One of these is the magnetic type which is typically used to fish the bottom of the well for junk comprised of ferrous metal. An example of this type of tool is shown in prior U.S. Pat. No. 2,834,630 to Greer. In this tool the magnet is floatingly mounted in a housing for rotational and limited longitudinal movement.
Another conventional type of junk basket is the circulation type in which drilling fluid is circulated through and around the tool to dislodge and pick up the junk and sweep it into the basket where it is retained. Some such tools operate by direct circulation while others operate by reverse circulation, and in either case, they are typically used for collecting relatively small or easily dislodged pieces of junk, whether ferrous or not.
Still another type of junk basket is the core cutting type, examples of which are shown in U.S. Pat. No. 2,471,616 and on page 2019 of the Composite Catalog of Oilfield Equipment and Services, 1964-65. Such tools include a cylindrical body open at the bottom and having teeth mounted around the lower end. Where the junk is large, tightly lodged in the well, and/or densely packed, this type of tool may be used to mill the junk or to cut a core through the junk. The core is received within the cylindrical body as the tool is urged downwardly and catchers are provided within the body to retain the core.
Each of these basic types of junk baskets is somewhat limited in its applications. Thus, where only such conventional tools are used, it is necessary to keep several types at the well site so that the proper one can be used as circumstances dictate. However, this is unduly expensive. Furthermore, it is often the case that one type of tool will be run into the well but will fail to satisfactorily remove the junk, so that it must be followed by a run of another type of tool. This makes the junk removal process quite time consuming and further increases the expense.
Several attempts have been made to provide a junk basket capable of removing junk by more than one technique. However, none of these have been entirely satisfactory. The 1964-65 Composite Catalog of Oilfield Equipment and Services, p. 2019 shows a magnetic type tool having milling teeth adjacent the magnet. However, these teeth could only be used to help dislodge and break up the junk which is to be picked up by the magnet and not to cut a core.
Prior U.S. Pat. No. 3,023,810 shows a junk retriever having a core cutting type of mechanism at its lower end as well as means for converting the tool from direct to reverse circulation. However, the circulation passages are formed in the tool by a number of different parts arranged in a rather complicated manner and in such a way that they might be relatively easily clogged.
Prior U.S. Pat. No. 2,710,741 to Hall also shows a fishing tool having core cutting and reverse circulation means. As in the tool of U.S. Pat. No. 3,023,810, the circulation passage system is relatively complicated and involves a number of different parts. Furthermore, the orientation of the passages is such as to create high turbulence in use and does not adequately direct the fluid in the desired paths. Finally, the tool must be adjusted for either direct or reverse circulation before it is run into the well and can not be altered downhole.
Still another combination type of junk basket is disclosed in the 1964-65 Composite Catalog of Oilfield Equipment and Services, pp. 736 and 738. The tool includes milling teeth and reverse circulation means which, once again, are unduly complicated and involve numerous parts. A magnet may be secured in the tool to convert it to a magnetic type of fishing tool. However, the magnet is not capable of augmenting or being used with the core cutting or reverse circulation techniques, but rather replaces them.